Fix cert-mon PriorityQueue regression in python3

In python3 the PriorityQueue raises an exception
due to

TypeError: '<' not supported between
        instances of 'SubcloudAuditData' and 'SubcloudAuditData'

The fix is to include a __lt__ method in SubcloudAuditData.
A timestamp field is added (primarily used in the tuple added to the
queue, but easy enough to include here) in order to aid in the sorting.

Test Plan:

PASS: trigger cert-mon audit for subclouds. Verify that the exception
is not raised, and that subclouds are properly enqueued for audit.

Closes-Bug: 1992680
Change-Id: Ibaa9a421eb809edc434793bc7e8ae92691be021f
Signed-off-by: Kyle MacLeod <kyle.macleod@windriver.com>

sysinv/sysinv/sysinv/sysinv/cert_mon/subcloud_audit_queue.py

@@ -25,15 +25,19 @@ LOG = log.getLogger(__name__)
 
 class SubcloudAuditData(object):
     """Representation of a subcloud under audit.
-    The 'name' field is used for all comparisons.
     """
     def __init__(self, name, audit_count=0):
         self.name = name
         self.audit_count = audit_count
+        self.timestamp = 0
 
     def __eq__(self, other):
         return self.name == other.name
 
+    def __lt__(self, other):
+        """Used in sorting the PriorityQueue"""
+        return self.timestamp < other.timestamp
+
     def __hash__(self):
         return hash(self.name)
 
@@ -81,6 +85,7 @@ class SubcloudAuditPriorityQueue(PriorityQueue):
 
         # this PriorityQueue is ordered by the next timestamp:
         sc_audit_item.audit_count += 1
+        sc_audit_item.timestamp = timestamp
         self.put(
             (timestamp, sc_audit_item)
         )